Direct heating of blast furnace air blast



Oct. 3, 1961 o. R. RICE 3,002,738

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3,002,738 DIRECT HEATING F BLAST FURNACE AIR BLAST Owen R. Rice,Pittsburgh, Pa., assignor to Koppers Company, Inc., a corporation ofDelaware Filed Oct. 3, 1958, Ser. No. 765,192 9 Claims. (Cl. 266-30) Thepresent invention relates in general to an improved system for heatingthe blast air for blast furnaces, and more particularly, to the directheating of air being delivered from the hot blast stoves to blastfurnace tuyeres by presently existing hot blast temperature controlsystems to raise the temperature of the hot blast air from conventionalstoves to a level above that which they now can be heated in existinghot blast stoves.

In many existing plants it is now possible to operate their blastfurnaces with a hotter blast than can be provided by their hot blaststoves. Such stoves are usually designed to preheat the blast air forthe blast furnace to a maximum temperature, say 1500 F., and it is nowdesired to heat this hot blast still higher, say to 1800"- 2000 F., in asimple way, since it is impractical to re construct the stoves forattaining this slightly higher preheat temperature therein and to alterthe control system in a complex way for the purpose.

A primary object of the present improvement is to retain the present hotblast stoves intact without change, as well as the present controlsystem therefor, and augment the heat in the blast by burning of naturalgas or coke oven gas directly into the preheated air from the stoves toraise its temperature further before it enters the tuyeres of the blastfurnace.

A further object of the invention is to attain this improvement in thefurther heating of the hot blast air for the furnace by utilizing partof the total air intended for support of the combustion of the fuel inthe furnace, directly in the hot blast from the stoves and before thefurnace tuyeres, so that the total air for the blast furnace remains thesame while the products of combustion of the gas in the hot blast, COand H 0, react with carbon in the furnace, producing useful reductantsin the blast furnace process.

The presently existing equipment in general comprises: a blast furnacewith tuyeres, a blower for supply of the total air for the blastfurnace, stoves for preheating the blast, a hot blast main leading fromthe stoves to the tuyeres, a cold blast main leading from the blower tothe stoves with a snort valve in the line and a bypass mixer lineleading around the stoves from a point in the cold blast main betweenthe snort valve and the stoves to the hot blast main from the stoves,either in the combustion chamber for the stoves or a point in the hotblast main after the combustion chamber.

The stoves are generally in sets of three, so that when one stove ispreheating the air for the blast, the other stoves are being heated upby combustion of gas in the combustion chambers for the stoves. Thetemperature of the stoves drops gradually as heat is absorbed from themin preheating the air, and to maintain a constant temperature in the airentering the tuyeres, part of the total air is fed around the stovesthrough the by-pass mixer line which mixes the cold air from the coldblast main with the hot blast air from the stoves to maintain the air inthe hot blast main at a constant temperature notwithstanding the gradualdrop in the temperatures of the stoves during their preheating of theair.

To this end, a thermocouple in the hot blast main or line operates acontrol in the furnace area control station to operate butterfly va vesin the bypass line and in the portion of the cold blast main or lineafter the nth take region of the by-pass mixer line so that less air rmPatent 3,002,738 Patented Oct. 3, 1961 flows through the mixer line andmore air through the stoves as their temperatures drop, thus keeping thetemperature of the preheated air constant in the 'hot blast line ormain. The blast furnace operating personnel can release the pressure inthe blast furnace by operating the snort valve which exhausts air fromthe blower to the atmosphere from the cold blast line or main in advanceof the by-pass mixer line and the stoves.

In accordance with the present invention, to raise the temperature levelof the hot blast from the stoves without alteration of the presentlyinstalled equipment for blast furnace systems, a temperature augmentingair line is connected to the cold blast main or line after the snortvalve to feed part of the total air to an air manifold, and a fuel gasline with a compressor is connected to feed fuel gas to a manifold,around the hot blast main. This air is a part of the total air from theblower and so the total air for the blast furnace remains the same.These manifolds feed burners which discharge into the hot blast main orline.

The temperature augmenting air line is provided with a butterfly valveand an orifice plate operatively connected together under control of anelement 9' in the furnace area control station 8 to adjust the air forthese burners. Feed of air and gas to these burners is constant, whereasthe butterfly valves for the by-pass mixer line and for the cold blastmain or line to the stoves are adjusted from a control station under theimpulse of the thermocouple in the hot blast line from the stoves whichis located therein before the burners for the temperature augmenting airline.

Preferably, the temperature augmenting air line leads off from the coldblast line at the region between the bypass mixer line and the rest ofthe cold blast line to the stoves.

Other objects and advantages of the invention will be apparent as it isbetter understood from the following description when considered inconnection with the accompanying drawings illustrating the best mode ofpracticing the same:

FIGURE 1 is a simplified diagrammatic plan view of a blast furnaceheating system embodying the present improvement;

FIGURE 2 is a more detailed schematic plan view illustrating the same;

FIGURE 3 is a top plan view illustrating the piping and stove and burnerarrangement of a plant embodying the invention;

FIGURE 4 is a vertical cross-section taken on the line 4-4 of FIGURE 3,showing the by-pass mixer line hookup;

FIGURE 5 is a vertical cross-sectional view on line 5--5 of FIGURE 3,illustrating the temperature augmenting air line hookup;

FIGURE 6 is a vertical cross-sectional view on the line 66 of FIGURE 3,showing the augmenting burner;

FIGURE 7 is a vertical cross-section through part of the burner ofFIGURE 5.

The same reference numerals are used for like parts in each of theseveral views.

Referring to the drawings, there is shown a typical existing blastfurnace system comprising the blast furnace proper 10, stoves 11, and ablower 12 for supply of the total air in a line 9 for the furnace. Theblower 12 is located in a central control station 8 and the air afterpreheating is fed to the furnace through a hot blast main 13. The hotblast main delivers the blast to a bustle pipe 14 which feeds the air tothe tuyeres 15 in the blast furnace. The cold blast air main 9 deliversthe total air for the blast furnace past a snort valve 16 to a by-passmixer line 17 and line 18 beyond the same leading to the stoves. Asshown, the stoves are heated up by combustion chamber 19 in alternationwith the preheating of the air, which air leaves the stoves through thecombustion chamber 19 as the entering part of the hot blast main 13. Theby-pass mixer line 17 discharges into the combustion chambers 19 of thestoves 11 seriatum, when they are operable for preheating of the blastto temper the heat of the air to a constant temperature as it flowsthrough the hot blast line 13 to the bustle pipe 14.

The lines 17 and 18 are provided with valves 20, 20 to control theproportions of the total volume of air that flows to the stoves 11 andaround the stoves to mix with the air from the stoves, to maintain thehot blast temperaure constant. These valves 20, 20 are controlled bythermo-responsive means in the form of a thermocouple 21 in the hotblast line 13 with connections to the valves 20, 20 to open the valve20' in the line 18 to the stoves and correspondingly close the valve 20in the by-pass mixing line 17 as the temperature of the air in the hotblast line drops. This mechanism 21 is adjusted by controls in thefurnace area control station.

The air from the mixer line 17 enters the combustion chambers 19 throughbranches 17 In accordance with the present invention, a direct heatingburner 22 is located in the hot blast line or main 13 directly beforethe bustle pipe 14, which comprises a special burner assembly with cokeoven gas burners 23. Combustion air for supporting this combustion issupplied to the burners 23 from the cold blast main 9 before the line 18to the stoves 11, and preferably from a region in the cold blast line 9between the by-pass line 17 and the snort valve 16, by a temperatureaugmenting air line 24 which terminates in an air manifold 24' for thecoke oven gas burners 23. The temperature augmenting air line 24 isprovided with a butterfly valve 25 and an orifice plate .26 withconventional means 27 for operating the valve 25 by and in accordancewith changes in pressure across the orifice plate 26.

The means 27 is a volume proportioning control that senses the impulsefrom line 9' and 24 and which operates the butterfly valve 25 tomaintain a constant pro portion of combustion air to the coke oven gasburners 23 in relation to the total blast air in line 9'. The volume ofthe total cold blast air in line 9 is measured by the existing orificeplate and volume measuring equipment 9" at the blower house 8, and theimpulse from the existing orifice plate at 9 is transmitted by way ofline 9a to the volume proportioning control 27. The volume of air inline 24 is measured by the orifice plate and measuring equipment at 26,and the impulse thereof is transmitted by line 26' to the volumeproportioning control 27 Fine manual adjustment of the volumeproportioning control 27 is based upon the temperature readings of fourthermocouples 28 in the tuyere stocks of the blast furnace. Coke ovengas is admitted to the gas burners 23 of burner 22 through a line 29 bya flow control valve 31 in proportion to the combustion air, in responseto a fuel-toair ratio controller 30 receiving its impulses by lines 26'and 37 from the orifice plate 26 in the combustion air supply line 24and line 29' from an orifice plate and measuring means 29" for measuringthe volume of coke oven gas in the output line 29. The output signal ofthe fuel to air ratio controller 30 by way of conduit 30 actuates thereverse acting by-pass valve 31 on a special positive displacement cokeoven gas compressor 32 which feeds gas by line 32 to a pulsationdampener 50. The compressor is a reciprocating type which requires apulsation dampener to smooth out pressure surges and is of the constantspeed, constant volume and constant discharge pressure type. A safetyshut-off valve 33 is placed in the section 34 to the coke oven gascompressor which is actuated by pressure switches 35, 35 in the hotblast main 13 and the line 29, to close upon failure of pressure in thecold blast main 9 and in the gas line 29 to the burner 22, as when thegas compressor discharge pressure drops. An override control 36,actuated by pressure switch 36', acts on the mechanism for opening thevolume proportioning butterfly valve 25 in the combustion air-supplyline 24 to hold the butterfly valve 25 in the line 24 from closing belowa preset minimum flow through this line, to suit the minimum turndownrate of the coke oven gas burners 23. ?ressure-sensitive switches 35,35' actuate solenoid valve 54 by way of conduits 52. The coke oven gasfrom compressor 32 not used in the system is released by valve 31 and byway of line 55 goes to a gas cooler 56 which then permits the gas to gothrough the conventional by-product recovery and disposal operation forthe coke oven gas. operation of this invention and, therefore, is notincluded. The fluctuations of a relief valve 57 also provides for therelease of the gas by way of lines 58 and 59 to cooler 56. Upon theactuation of valve 33, coke oven gas is fed directly through lines 34and 60 to cooler 56.

The invention is herein-above set forth as embodied in a particular formof construction but may be variously embodied within the scope of theclaims hereinafter made.

I claim:

1. In a blast furnace system, the combination with a blast furnacehaving tuyeres, a blower for supply of the total air for the blastfurnace, stoves for preheating the blast, a hot blast main line leadingfrom the stoves to the tuyeres, a cold blast air line leading from theblower to the stoves with a snort valve in the line and a by-pass mixerline leading around the stoves from a point in the cold blast air linebetween the snort valve and the stoves to a point in the hot blast lineafter the stoves, throttle valves in the portion of the cold blast lineafter the snort valve which leads to the stoves and in the by-pass mixerline for regulating the volumes of air flow through said line portionand said by-pass line, and thermo-responsive means operable by thetemperature dilferences in the hot blast line for adjusting the throttlevalves as the stove temperatures drop, to maintain a constanttemperature of the air in the hot blast line leading to the tuyeres, anda central control for operating said blower, snort valve, andthermo-responsive means of a burner set for burning gas directly intothe air in the hot blast line at a point therein after saidthermo-responsive means, a temperature augmenting air line leading froma point in the cold blast line after the snort valve to said burner forsup porting combustion of fuel therein to raise the temperature of thehot blast air to a level above the possible maximum preheat of the airin the stoves, means for supplying fuel to said burner for combustiontherein with said air, and a volume proportioning valve in saidtemperature augmenting air line and actuating means therefor operable byand in accordance with changes in rate of flow of the total air enteringthe blower aforesaid and responsive to change in rate of flow in saidaugmenting air line for actuating said volume proportioning valve, tomaintain constant the proportion of air fed to said burner by saidaugmenting air line in relation to the aforesaid total air entering theblower.

2. A blast furnace system as claimed in claim 1, and in which theaugmenting air line leads off from the cold blast air main after thesnort valve and before the bypass line.

3. A blast furnace system as claimed in claim 1, and which includes aconstant speed, constant volume and constant discharge pressure meansfor compressing the gas for said burner; a fuel-to-air ratio controlleroperable by and in response to change in rate of flow in the augmentingair line to the burner, to control the volume of gas from the compressorto said burner; a safety shutoff valve on the suction side of said gascompressor with a pressure switch in the hot blast main operativelyconnected with the shut-off valve to close the same upon failure ofpressure in the cold blast main, and a control on, the vol meproportioning valve for the augmenting The latter equipment is not-an rair line, to close the same at a preset minimum flow through the line tothe minimum turndown rate of the fuel burner.

4. A blast furnace system as claimed in claim 1, and which includesmeans for compressing the gas for said burner; a fuel-to-air ratiocontroller operable by and in response to change in rate of flow in theaugmenting air line to the burner, to control the volume of gas from thecompressor to said burner; a safety shut-off valve on the suction sideof said gas compressor with a pressure switch in the hot blast mainoperatively connected with the shut-off valve to close the same uponfailure of pressure in the cold blast main.

5. A blast furnace system as claimed in claim 1, and which includesmeans for compressing the gas for said burner; and a fuel-to-air ratiocontroller operable by and in response to change in rate of flow in theaugmenting air line to the burner, to control the volume of gas from thecompressor to said burner.

6. In a blast furnace system, the combination with a blast furnacehaving tuyeres, a blower for supply of the total air for the blastfurnace, stoves for preheating the blast, at hot blast main line leadingfrom the stoves to the tuyeres, a cold blast air main line leading fromthe blower to the stoves with a snort valve in the line and a by-passingmixer line leading around the stoves from a point in the cold blast airmain line between the snort valve and the stoves to a point in the hotblast line after the stoves, throttle valves in the portion of the coldblast line after the snort valve which leads to the stoves and in theby-pass line, for regulating the volume of airflow through saidportions, and thermo-responsive means operable by the temperaturedifferences in the hot blast line for adjusting the throttle valves asthe stove temperatures drop, and a central control for operating saidblower, snort valve, and thermo-responsive means, of a burner set forburning gas directly into the air in the hot blast line at a pointtherein after said thermo-responsive means, a temperature augmenting airline leading from the cold blast main line after the snort valve to saidburner for supporting combustion of fuel therein to raise thetemperature of the hot blast air to a level above the preheat of the airin the stoves, means for supplying fuel to said burner for combustiontherein with said air, and a volume proportioning valve in saidtemperature augmenting air line and actuating means therefor operable byand in accordance with changes in rate of flow of the total air enteringthe blower aforesaid and responsive to changes in rate of flow in saidaugmenting air line for actuating said volume proportioning valve, toregulate the proportion of air fed to said burner by said augmenting airline in relation to the aforesaid total air entering the blower.

7. A blast furnace system as claimed in claim 6, and which includes aconstant speed, constant volume and constant discharge pressure meansfor compressing the gas for said burner; a fuel-to-air ratio controlleroperable by and in response to change in rate of flow in the augmentingair line to the burner, to control the volume of gas from the compressorto said burner; a safety shutoff valve on the suction side of said gascompressor with a pressure switch in the hot blast main operativelyconnected with the shut-off valve to close the same upon failure ofpressure in the cold blast main, and a control on the volumeproportioning valve for the augmenting air line, to close the same at apreset minimum flow through the line to the minimum turndown rate of thefuel burner.

8. A blast furnace system as claimed in claim 6, and which includesmeans for compressing the gas for said burner; a fuel-to-air ratiocontroller operable by and in response to change in rate of flow in theaugmenting air line to the burner, to control the volume of gas from thecompressor to said burner; and a safety shut-off valve on the suctionside of said gas compressor with a pressure switch in the hot blast mainoperatively connected with the shut-off valve to close the same uponfailure of pressure in the cold blast main.

9. A blast furnace system as claimed in claim 6, and which includesmeans for compressing the gas for said burner; and a fuel-to-air ratiocontroller operable by and in response to change in the rate of flow inthe augmenting air line to the burner, to control the volume of gas fromthe compressor to said burner.

References Cited in the file of this patent UNITED STATES PATENTS1,010,490 Prick Dec. 5, 1911 1,816,174 Brown July 28, 1931 1,977,559Lewis et a1. Oct. 16, 1934 2,142,100 Avery Jan. 3, 1939 2,625,386 LeoneJan. 13, 1957 2,833,643 Newman May 6, 1958 FOREIGN PATENTS:

78,964 Switzerland Sept. 17, 1918 582,429 Great Britain Nov. 15, 1946691,923 Great Britain May 27, 1953

